Under the hammer will be a 1.5kg white truffle, the largest ever found, and bidding is expected to top £100,000 - making it gram for gram more expensive than gold.

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The auction, overseen by Sotheby's, will take place simultaneously at three locations.It will link up Giorgio Locatelli's Refettorio near Blackfriars with the Palazzo Medici in Florence and The Grand Lisboa in Macao.

The truffle was unearthed in hills near Pisa this month. It was then taken to Rome where it was officially weighed and flown to Macao for the sale.

Previously, the largest white truffle weighed in at 1.3kg and was found in Croatia in 1999.

The record-breaking truffle was found by Cristiano Savini and his dog Rocco. He spent more than two hours carefully digging it out of the ground so as not to damage it.

Mr Savini said: "Rocco just went crazy and I had to tie him up because he was so excited. As the news spread I had ridiculous offers for the truffle - someone offered me £70,000. I decided that the best thing to do was put it up for auction.

"My family has been truffle hunting for the last four generations and the emotion I felt when I found this beauty was so intense."

Auction organiser Giselle Oberti said: "The price we are aiming for is £100,000 and the money will go to various children's charities. We have more than 200 people at the three locations."